The present invention relates to a chain conveyor of the type comprising a first and a second link chains sliding within guides, in which the annular elements of a chain are connected to corresponding annular elements of the other chain by cross bars, and in particular is concerned with improvements to the devices for entraining or driving the chain belts of the abovementioned conveyor.
Chain conveying systems are known for example from DE-U-8623146, EP-A-274751 and EP-A-275562. Conveying systems of this kind have proved to be particularly useful in many sectors on account of their versatility of use and the significant constructional simplification of these conveyors compared to other conventional conveying systems.
In particular, a chain conveyor comprises a first and a second endless chains formed by interlinked annular elements slidable in respective longitudinal channel guides defining the path of the conveyor; the annular elements of a chain are connected to corresponding annular elements of the other chain by means of cross bars which define the surface of the conveyor belt.
In chain conveyors of the abovementioned kind, the belt is entrained and moved by means of drive units each comprising sprockets or toothed wheels engaging with one or both of the chains of the belt, to cause them to move forward at the desired speed.
The toothed wheels generally engage tangentially and underneath the chain, being arranged in a vertical plane passing through the chain itself.
Such entrainment systems involve considerable drawbacks and limitations as regards use of the conveyor, associated mainly with the small dimensions and arrangement of the toothed wheels which do not allow uniform entrainment.
In fact, the vertical disposition of the toothed wheels and tangential engagement of the latter with the chains causes a continuous up-down movement raising and lowering the chains in the region of each driving unit, which is damaging for many reasons. In particular, the frequent raising and lowering movement of the chains, in addition to producing a considerable amount of noise, gives rise to vibrations over the entire belt, vibrations which may be damaging in the case where the conveyor is used for example to convey baking products inside leavening chambers.
In order to oppose the raising and lowering movement of the chains and limit the vibrations of the belt, usually it is necessary to use guide rails which oppose raising of the chains in the region of each drive unit. This results in a substantial power loss owing to the significant amount of friction produced by the chains rubbing against the guide rails; it has been noted, in fact, that about 50% of the power used in each driving unit is normally lost owing to rubbing of the chains against the channel guide of the conveyor belt.
In many application sectors, in particular in the confectionery and bakery industries, there is also the need to use multiple turns conveyors where the conveyor belt extends in the manner of superimposed turns, for example for the purpose of conveying and transporting the product inside a leavening or freezing chamber, or in order to cool the product to ambient temperature after it has left the oven.
Normally the drive units are positioned in rectilinear zones of the belt so as to allow correct meshing with both chains, by the toothed wheels. For reasons of dimensions, circular turns are also required, which giving rise to the need for a drive unit performing the entrainment at the entry point since there are no straight sections available. In such a case, a single toothed wheel is used on the outer side chain of the belt.
In all cases there is a need for the longest possible conveying path in keeping with the volume of the chamber in which the conveyor is installed or working environment in which a similar conveyor is located.
It would therefore be desirable to arrange the multiple runs of the conveyor in superimoposed planes located very close to one another, so as to limit the height dimensions and consequently the volumes of the leavening or freezing chamber, namely to achieve longer conveying paths for the same conveyor dimensions.
There is, however, a limit as to the amount by which the space between the turns or runs of conventional chain conveyors can be reduced, owing to the dimensions imposed by the toothed entrainment wheels which are provided between adjacent turns of the belt. Reducing the diameters of the entrainment wheels so as to be able to bring the planes of the conveyor turns closer together is in practice not possible since it would result in further irregularities in feeding of the belt which are unacceptable for the intended applications; furthermore, the minimum dimensions of the toothed wheels are bound by the dimensions of the chain link.
A first object of the present invention is to provide a chain conveyor of the kind mentioned, above provided with an improved drive unit to be applied to any type of chain conveyor independently of the path followed by the conveyor belt, by means of which the raising and lowering movement of the belt is totally eliminated, with consequent elimination or reduction in the noise and vibrations to which conventional chain conveyors are usually subject. In this way a chain conveyor is obtained, which is provided with a belt entrainment device able to ensure a high degree of regularity of movement.
A further object of the present invention is to provide a chain conveyor having an improved drive device for the chain belt by means of which it is possible to exploit most of the power supplied by the motor for driving the belt, after substantially eliminating many of the causes of friction, at speeds even greater than those of conventional conveyor belts owing to the possibility of using toothed wheels of larger diameters, without substantially increasing the overall dimensions of the conveyor, but on the contrary reducing them.
A further object of the present invention is to provide a chain conveyor of the kind mentioned above, in particular a multiple runs conveyor, provided with a drive device by means of which it is possible to substantially reduce the space between turns compared to a conventional conveyor.
Yet another object of the present invention is to provide a drive device for chain conveyors, as referred to above, by means of which it is possible to provide circular or curved paths which, for belts having the same width, have comparatively smaller radii of curvature or, for the same radius of curvature, may permit belts having greater widths.
Yet another object of the invention is to provide a drive device such as to allow lateral extension of the cross bars connecting the chains of the conveyor belt, beyond the chains and guides, thus enabling chain belt conveyors with different belt widths to be constructed, independently of the space between the guides for the chains of the same belt.
These and other objects of the invention can be achieved in chain conveyors comprising drive devices according to claim 1 which is characterised by a special arrangement of the entrainment toothed wheels in each drive unit, namely by a particular embodiment and/or disposition of the drive device itself.